1. Technical Field
The present invention relates to a method for producing of a polybenzoxazole precursor, which uses a water-insoluble solvent and water for extraction in purification of a polybenzoxazole precursor, thereby reducing impurities such as residual halogen and residual aprotic polar solvent, and the like.
2. Description of Related Art
Polybenzoxazoles possess superior properties such as high heat resistance and mechanical characteristics, because of its rigid main chain structure like polyimide resins, and therefore are a material that can be applied to various electronic devices. A polybenzoxazole precursor has been attracted attention because it has a phenolic hydroxy group in its structural unit and can easily form a clear fine positive pattern by alkali development when being combined with a diazonaphthoquinone compound.
As a method for synthesizing a polybenzoxazole precursor is cited a method which comprises reacting aromatic dicarboxylic acid dihalide and bis(o-aminophenol) in an aprotic polar solvent. This synthesis method, however, necessarily allows a large amount of halogen component to remain in a polymerization solution. Therefore, particularly when the resultant polybenzoxazole is used for an electronic material, such residual halogen must be completely removed because it may cause serious problems for electronic wiring.
Although a method in which a treatment of washing a polybenzoxazole precursor with pure water or an alcohol is repeated has been commonly used, it has been difficult to completely remove residual halogen in the polybenzoxazole precursor. Japanese Patent Application Laid-Open No. 2007-106786 discloses a method which comprises dropping a polybenzoxazole precursor solution into water and then performing water washing treatment and aqueous alkali solution washing treatment. This method, however, induces generation of a large amount of waste water. Moreover, since an aprotic polar solvent to be used as a solvent for synthesis strongly associates with a solute polybenzoxazole precursor, it is difficult to remove residual aprotic polar solvent, leading to some problems, for example, a problem that a uniform film cannot be obtained in molding or coating.